Gamma ray detector



March 9, 1954 M. EVANS 2,671,868

GAMMA RAY DETECTOR Filed April 1l, 1950 TTOKNEHS' Patented Mar. 9, 1954 GAMSMA RAY DETECTOR Leon M. Evans, Houston, Tex.. assignor to The Texas Company, New York, N. Y.,l a corporation oftDelaware Application April 11, 1950;. Serial No. 155,256;

2 Claims.

I'his invention relates to radiation detectors and more particularly to gamma ray detectors of the counter or pulse type. The principal object of the invention is the provision of such a detector which will have a higher efciency for detecting gamma raysV than those instruments which are now available.

As is well known to those generally familiar with this art` a conventional Geiger-Mueller counter usually comprises a sealed glass envelope adapted to contain an ionizable gaseous medium, a. cathode and an anode., The cathode is usually in the form of a thin metallic cylinder and the anode comprises a fine wire stretched along the longitudinal axis of the cylinder and a high potential is impressed across the cathode and the anode through a resistor. Normally the potential difference between, the cathode. and the anode is nearly but not quite high enough to cause an electrical discharge to take place. If a gamma ray strikesthe cathode cylinder an electron may be ejected into the gas thus producing ionization and a discharge or pulse with a current flow of the order of a few microamperes. This causes a` rather large voltage drop across the resistor byr suitably amplifying this voltage drop a mechanical recorder or other device capable of registering the dischargesmay be actuated.

InA the U. S. Letters Patent-No. 2,397.0 73- granted March 19, 1946-, to` D. G. C'. Hare and Gerhard Herzog a gamma ray counter is disclosed which has several times the e'ciency of the above descri-bed conventional counter. The counterv described in the patent comprisesy a plurality of cathode sheets or plates disposed in parallell spaced relation with one or more anode wires disposed between and parallel to adjacent pairs of cathode plates. In this manner a much greater effective cathode area or surface can be disposed in the same volume or in a housing or envelope as would be used in a conventional counter of the same dimensions and thus a much greater effective cathode surface area will be exposed to the same gamma radiation, thus providing an increase in efciency over the conventional counter depending generally upon the increase in cathode area of the parallel plates over the area of the cathode cylinder in a conventional counter.

Again in the U. S. Letters Patent N o. 2,397,071 granted to D. G. C. Hare, March 19, 1946, another highly eicient gamma ray counter is disclosed in which the cathode comprises a plurality of parallel spaced thin metallic plates or discs, the bank of plates being provided with one or more series of aligned holes with an. anode wire. extending along the longitudinal axis ci. each series4 of holes. In comparing a counter of this. type with a. conventional counter of the same external, dimensions, the counter as disclosed in. the patent will have a much greater effective surface area, exposed to. the gamma. radiation. than will the conventional, counter and the eiiciency of the patented counter isk therefore usually several times that. of the` conventional counter.

In accordance with the present invention. a counter is. provided generally of the type disclosed in the aboveV mentioned patents, that is,v

having a4 plurality of spaced parallel. cathode plates but in which the effective cathode plate area is still. further increased by roughening the surface which is. exposed. to the gas lling..` In the preferred embodiment the cathode platesf areY formed of a porous metallic materialA such as. a sintered compressed metal powder. The sur-- face of such material is, as is. shown, by the mi.- croscope, very rough and a meta-1 surface is thus presented. to the surrounding gas which is much greater than would be presented by a smooth., metal plate of.- the same dimensions..

For a better understanding of the invention. reference may be had to the accompanying draw-y ing which:

Figure 1 is. a somewhat, diagrammatic vertical sectionalielevation through a. conventional. gamma ray counter;

Figure 2 is a diagrammatic elevation of the. cathode and anode arrangement in one form of multiplate counter;

Figure 3' is a planned View of a cathode plate having a roughened surface, and

Figure 4 is an enlarged cross section of a small section of the plate of Figure 3 such as is indicated at A.

Referring to Figure 1 of the drawing a cylindrical cathode formed of a thin metal sheet I0 is shown as disposed within a sealed glass envelope I2. An anode wire I4 is disposed along the longitudinal axis of the cathode and may be supported by sealing it into the ends of the envelope l2. The cathode I0 may be formed of any suitable metal such as brass and the envelope l2 is filled with a suitable gas such as argon at a pressure about atmospheric. A high voltage is connected across the cathode I0 and the anode i4 through a resistor R. When a gamma ray strikes the cathode I0 it may eject an electron therefrom so as to ionize the gas within the counter housing thus causing a dis charge which may be measured or determined by measuring the voltage drop across the resistor R by any suitable circuit means.

In Figure 2 is shown diagrammatically a cathode comprising a plurality of thin metallic plates or discs I6 disposed in parallel spaced relation as is disclosed in the aforementioned Hare Patent No. 2,397,071. Each of the cathode plates is provided with one or more holes I8, four being shown in this example and the plates are oriented in a suitable housing or envelope not shown so that the holes in the plates will be aligned in several series. An anode wire 20 is disposed along the axis of each series of holes and the anode wires may be connected together electrically as shown. 'Ihe cathode plates are also connected together electrically. The lead wires 22 and 24 may be connected on Figure 1 to a suitable source of high voltage and a resistor.

In Figure 3 one of the cathode plates I8 is illustrated and in Figure 4 is illustrated an enlarged cross section of a small portion of the plate such, for instance, as that indicated at A in Figure 3.

In the preferred embodiment of the invention the cathodes of the counters such as those shown in Figures 1 and 2 may be formed of a porous metallic material such as the sintered compressed metal powder known as Oilite which has been previously employed as a bearing material. The metal which in powdered form is used in the manufacture of this material may be, for example, brass or Phosphor bronze. This material is generally available in two or more qualities one of these having a density of 5.8 and another of 2.6 grams per cubic centimeter. These materials have a relatively high ratio of surface area to volume and as is shown diagrammatically in Figure 4 the surface is generally quite rough even to the naked eye. Under the microscope the metal particles from which the sheet material is formed are shown to present a multitude of tiny projections and thus a very large surface area is presented to the gas which will be in contact with the plates when they are disposed within a counter housing. A gamma ray counter which was made in the form shown in Figure 2 using cathode plates formed of this sintered compressed metal powder showed an e'iciency of 15 to 20% higher than a counter using smooth brass plates of the same number and size. By selecting the plate material to have a very large surface area to volume ratio this increase in eiciency can be considerably higher.

Although the cathode plates illustrated in Figures 2 and 3 are in the form of thin discs, it is to be understood that these plates may also be in other shapes such as the cylinder l0 shown in Figure 1 or the elongated rectangular sheets such as are disclosed in the aforementioned Hare and Herzog Patent No. 2,397,073.

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A gamma ray detector comprising a sealed housing adapted to contain a gas filling, a cathode disposed in said housing formed of at least one thin metal plate and an anode wire disposed in proximity to said cathode so as to provide for a concentration of an electric eld, said cathode plate being formed of a sintered, compressed metal powder so that its surface will be rough to present a greater surface area than a smooth plate of the same dimensions.

2. A gamma ray detector comprising a sealed housing adapted to contain a gas filling, a plurality of thin parallel spaced metal plates connected together electrically to form a cathode within said housing, said plates being provided with at least one series of aligned holes and an anode wire disposed axially through said series of holes, said plates being formed of a sintered, compressed metal powder so that the plate surfaces will be rough and will present a greater Surface area than would be presented by smooth plates of the same dimensions.

LEON M. EVANS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,492,464 Jacobus Apr. 29, 1924 2,218,076 Werner Oct. 15, 1940 2,367,939 Gregory Jan. 23, 1945 2,397,661 Hare Apr. 2, 1946 2,437,576 Wick Mar. 9, 1948 2,473,550 Spencer June 21, 1949 2,486,944 Hare Nov. 1, 1949 2,512,769 Crumrine June 27, 1950 2,543,728 Lemmens et al Feb. 27, 1951 OTHER REFERENCES Increased Gamma-Ray Sensitivity of Tube Counters and the Measurement of the Thorium Content of Ordinary Materials by Evans and Mugele, from Review of Scientific Instruments, December 1936, pp. 441-449. 

1. A GAMMA RAY DETECTOR COMPRISING A SEALED HOUSING ADAPTED TO CONTAIN A GAS FILLING, A CATHODE DISPOSED IN SAID HOUSING FORMED AT LEAST ONE THIN METAL PLATE AND AN ANODE WIRE DISPOSED IN PROXIMITY TO SAID CATHODE SO AS TO PROVIDE FOR A CONCENTRATION OF AN ELECTRIC FIELD, SAID CATHODE PLATE BEING FORMED OF A SINTERED, COMPRESSED METAL POWDER SO THAT ITS SURFACE WILL BE ROUGH TO PRESENT A GREATER SURFACE AREA THAN A SMOOTH PLATE OF THE SAME DIMENSIONS. 